According to the prior art, the production of biodegradable fatty alcohols as raw material for example for the detergent industry is effected either by catalytic hydrogenation of breakdown fatty acids in a discontinuously operated reactor with catalyst slurry or continuously in a trickle-bed reactor with solid catalyst bed on the basis of methyl esters or wax esters of the corresponding fatty acids.
In the production of fatty alcohols by hydrogenation of methyl esters, fractions of non-converted methyl ester still are present in the produced fatty alcohol. During the hydrogenation, the throughput through the shaft or tubular reactor therefore already is adjusted such that only traces of methyl ester can be found in the exiting product stream, which ultimately limits the maximum possible throughput at the reactor. This procedure is necessary, since methyl esters of a certain C chain length n form azeotropes with the associated alcohols of the C chain length n−1, and the remaining methyl esters in the fatty alcohol mixture therefore cannot be separated completely by distillation.
In the patent EP 0 454 720 B1 of Davy McKee Ltd. a process is described, with which a large amount of the fatty alcohol can be recovered from a mixture of fatty alcohols (FA) and fatty acid methyl esters (ME). For this purpose, the FA/ME mixture initially is mixed with a homogeneous catalyst, preferably an alkyl titanate, and a transesterification of the ME to wax esters (WE) and methanol (MeOH) is carried out. After reaching the chemical equilibrium, the product mixture which now contains FA, WE, MeOH and small traces of ME is liberated from MeOH by distillation. The residue of FA, WE and small traces of ME obtained by distillation subsequently is liberated from a large amount of the contained FA in a further distillation. The residue of the second distillation now is again mixed with MeOH and subjected to a second transesterification, in which FA and ME again are obtained from the contained WE together with MeOH. The used excess of MeOH is separated from the obtained reaction product by evaporation, and the latter is fractionated in a further distillation into a distillate comprising FA and ME as well as a distillation residue, which also contains the homogeneous catalyst used in the first step and is partly recirculated and partly disposed of. Thus, two reaction and four fractionation steps must be carried out in this process.
The unexamined German application DE 10 2007 033 636 A1 describes a production process for fatty alcohols by hydrogenation of fatty acid methyl esters and the separation of the fatty alcohol mixtures thus produced into individual fractions after the hydrogenation by distillation. In particular, there is taught a process for separating a lower alkyl ester of a fatty acid from a fatty alcohol fraction or from a fatty alcohol mixture. This object is solved in that the fatty alcohol fraction or the fatty alcohol mixture is transesterified to fatty alcohol (FA), wax ester (WE) and the lower alkyl alcohol and at the same time the lower alkyl alcohol is discharged from the reaction mixture substantially completely and the wax ester is separated from the obtained product. In particular, it is proposed to carry out the transesterification in the presence of a heterogeneous transesterification catalyst. In contrast to the homogeneous catalyst which is used in the process according to EP 0 454 720 B1, there is not obtained a catalyst-containing residue. The wax ester obtained is pure and free from catalyst and therefore can be recirculated to the hydrogenation of fatty acid alkyl ester without further purification or processing. In DE 10 2007 033 636 A1, there was preferably used a titanium silicalite catalyst.